Compensation Of Channel Non-Reciprocity In TDD MIMO Systems

As an effective way to achieve high data rates, MIMO technique has been widely studied and employed in new-generation of wireless communication systems. By exploring channel reciprocity in time division duplex(TDD) MIMO systems, base station(BS) can make transmit strategies according to the channel state information (CSI) through reverse link channel estimation. But channel estimation errors and radio frequency(RF) front-end imperfections will destroy channel reciprocity.This thesis analyzes the impact of channel estimation errors and I/Q imbalance on channel reciprocity in TDD-MIMO systems. In the thesis, channel estimation method based on time domain truncation and I/Q imbalance compensation algorithms are proposed. The main contributions are as follows:1. Several conventional channel estimation methods for MIMO-OFDM systems are studied and discussed, and the lose of channel reciprocity due to imprecise channel estimation is analyzed, a new channel estimation method based on time domain truncation is proposed. Simulation results show that the method can improve the performance with low complexity.2. The equivalent model of MIMO systems with I/Q imbalance in receiver is derived, the lose of channel reciprocity is analyzed in terms of system capacity, and one method for compensating channel non-reciprocity due to I/Q imbalance in receiver is proposed, simulation results show that the proposed method can improve BER performance and system capacity.3. The equivalent model of MIMO systems with I/Q imbalance in both transmitter and receiver is derived. Calibration algorithms with and without I/Q imbalance parameters are proposed respectively to compensate the loss of channel reciprocity. Simulation results show that the proposed algorithms significantly improve BER performance and system capacity.